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The Life of a Cell The Chemistry of Life Atoms and Their Interactions Elements • Everything – whether it is a rock, frog, or flower – is made of substances called elements. • Element: a substance that can’t be broken down into simpler chemical substances. It is made of one type of atom. Natural elements in living things • Of the naturally occurring elements on Earth, only about 25 are essential to living organisms. • Carbon, hydrogen, oxygen, and nitrogen make up more than 96 percent of the mass of a human body. Trace elements • Trace elements such as iron and copper, play a vital role in maintaining healthy cells in all organisms. • Plants obtain trace elements by absorbing them through their roots; animals get them from the foods they eat. Table 6.1 Some Elements That Make Up the Human Body Percent By Percent By Element Element Symbol Mass in Symbol Mass in Human Body Human Body Oxygen Fe O 65.0 Iron trace Zn Zinc Carbon C 18.5 trace Hydrogen Cu H 9.5 Copper trace I Iodine Nitrogen N 3.3 trace Calcium Ca 1.5 trace Manganese Mn Boron B 1.0 Phosphorus P trace Cr K Potassium 0.4 Chromium trace trace Molybdenum Mo Sulfur S 0.3 Cobalt Sodium Co trace Na 0.2 Se Chlorine 0.2 Selenium trace Cl Fluorine F Magnesium Mg 0.1 trace Atoms: The Building Blocks of Elements • Atom: the smallest particle of an element that has the characteristics of that element. • Atoms are the basic building blocks of all matter. The structure of an atom • Nucleus: the center of an atom • contain positively charged particles called protons (p+) • particles with no charge, called neutrons (n0). • Space surrounding the nucleus contains negatively charged particles called electrons (e-) The Structure of an atom Nucleus Electron energy levels The Structure of an atom • Protons and neutrons are approximately the same size and mass, however electrons are far smaller • Because opposites attract, the negatively charged electrons are held in the electron cloud by the positively charged nucleus. Electron energy levels • Electrons exist around the nucleus in regions known as energy levels. Nucleus 8 protons (p+) 8 neutrons (n0) Oxygen atom • First energy level can hold two e-. • Second level can hold a maximum of eight e-. • Third level can hold up to 18 e-. Electron energy levels • An atom of fluorine has nine electrons. How many electrons are in its second energy level? Electron energy levels • Atoms contain equal numbers of electrons and protons; therefore, they have no net charge. • If an atom of fluorine has nine electrons, how many protons are in an atom of fluorine? •How many e- does phosphorous (P) have? •How many p+ does P have? •How do you know? Isotopes of an Element • Atoms of the same element always have the same number of protons but may contain different numbers of neutrons. • Isotopes: atoms of the same element that have different numbers of neutrons • Carbon-12, carbon-13 and carbon-14 are examples of isotopes. Compounds and Bonding • Compound: a substance that is composed two or more different elements that are chemically combined. • Table salt (NaCl) Chemical formula is a compound composed of the elements sodium and chlorine. •Water (H20) Hydrogen and Oxygen by themselves are flammable – together they are stable… Bonds: Types and how they form • Atoms combine with other atoms to become more stable. • For many elements, an atom becomes stable when its outermost energy level is full. • Sharing electrons with other atoms is one way for elements to become stable. • Bonding is how they “share” • Covalent bond : an attractive force between two atoms that share electrons. • Molecule : a group of atoms held together by covalent bonds. It has no overall charge. Water molecule How covalent bonds form • Two hydrogen atoms can combine with each other by sharing their electrons. • Each atom becomes stable by sharing its electron with the other atom. Hydrogen molecule •Think: full outer shell Ionic bonds • An atom (or group of atoms) that gains or loses electrons and has an electrical charge and is called an ion. • Ionic bond : attractive force between two ions of opposite charge • Example: A chlorine atom becomes a chloride ion when it gains an electron. Hydrogen Bonds • biological bonds • Weak bonds (think magnet) between hydrogen (H+) and oxygen (O-). – Unequal sharing of electrons making it a polar molecule • Hydrogen bonds give water unique properties Hydrogen Bonds • Unique properties of water due to H bonds: • Universal solvent – Can bond with other water molecules and molecules of other substances • Water has a greater resists to changes in temperature (boiling and feezing) • Found in all 3 states: gas, a liquid, and a solid – Less dense when in a solid state • Helps in temperature regulation of all organisms on earth Bonds and Chemical Reactions • How are bonds and chemical reactions “related” ? •Chemical reactions occur when bonds are formed or broken. • causing substances to recombine into different substances (ex. burning paper). •What do you think “Drives” all the breaking and forming of bonds? •ENERGY!!! chemical reactions • In a chemical reaction there are two parts: Reactants and Products Chemical Reactions as Chemical Equations • 2H + O2 = H2O - chemical equation of Water •Chemical equations – Show bonds being broken and formed – They show the Law of Conservation of Mass (atoms are neither created nor destroyed in chemical reactions. They are simply rearranged.) Mixtures and Solutions • Mixture : a combination of substances in which the individual components retain their own properties. • Neither component of the mixture changes. – Salad, chex mix, sand and water Mixtures and Solutions • Solution : a mixture in which one or more substances (solutes) are distributed evenly in another substance (solvent). • Kool-aid, hot coco Acids and bases • Chemical reactions can occur only when conditions are right. • A reaction may depend on: - energy availability - temperature - concentration of a substance - pH of the surrounding environment Acids and bases • pH : a measure of how acidic or basic a solution is. • A scale with values ranging from below 0 to above 14 is used to measure pH. More acidic Neutral More basic Acids and bases •pH below 7 are acidic. •Acid : any substance that forms hydrogen ions (H+) in water More acidic Neutral More basic Acids and bases • Substances with a pH above 7 are basic. •Base : any substance that forms hydroxide ions (OH-) in water. pH 11 The Life of a Cell The Chemistry of Life Organic Compounds: Macromolecules The Role of Carbon in Organisms • Carbon compounds that come from living organisms are called organic compounds. • Two carbon atoms can form various types of covalent bonds—single, double or triple. Molecular chains • The small molecules, monomers, bond together to form large chains called polymers. • Polymer : a large molecule formed when many smaller molecules bond together. • Polymers usually form by covalent bonding. • There are 4 main organic compounds – Charbohydrates – Poteins – Lipids – Nucleic Acids The structure of carbohydrates • Carbohydrate : composed of carbon, hydrogen, and oxygen with a ratio of about two hydrogen atoms and one oxygen atom for every carbon atom. The structure of carbohydrates • Monosaccharide : the simplest type of carbohydrate; a simple sugar (ie. glucose, fructose) • Glucose and fructose combine in a condensation reaction to form sucrose (table sugar) • Which is the reactant and which is the product? The structure of carbohydrates • The largest carbohydrate molecules are polysaccharides, composed of many monosaccharide subunits. (ie. potatoes, liver) • Which is the monomer? • Which is the polymer? The structure of lipids • Lipids : large biomolecules that are made mostly of carbon and hydrogen with a small amount of oxygen. (ie. fats, oils, waxes) The structure of lipids • They are insoluble in water because their molecules are nonpolar and hydrophobic • (hydro) (phobic) The structure of lipids • A fatty acid with single bonds is saturated; with double bonds is unsaturated The structure of proteins • Protein : a large, complex polymer composed of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur. The structure of proteins • Amino acids : the basic building blocks of proteins • There are about 20 common amino acids that can make literally thousands of proteins. The structure of proteins • Peptide bonds : covalent bonds formed between amino acids. The structure of proteins • Proteins are the building blocks of many structural components of organisms. • Enzymes are important proteins found in living things. • They speed the reactions in digestion of food. The structure of proteins • Enzyme : a protein that changes the rate of a chemical reaction. • The sum of all the chemical reactions occurring in an organism is Metabolism The structure of nucleic acids • Nucleic acid : a complex biomolecule that stores cellular information in the form of a code. • Nucleotides : small subunits that make up nuclei acids The structure of nucleic acids • Nucleotides are arranged in three groups—a nitrogenous base, a simple sugar, and a phosphate group. Phosphate Sugar Nitrogenous base The structure of nucleic acids • DNA, which stands for deoxyribonucleic acid is a nucleic acid. Phosphate Sugar Nitrogenous base The structure of nucleic acids • The information coded in DNA contains the instructions used to form all of an organism’s enzymes and structural proteins. • Another important nucleic acid is RNA, which stands for ribonucleic acid. RNA is a nucleic acid that forms a copy of DNA for use in making proteins.